Electric discharge devices



July 8, 1958 w. J. scoTT ET AL 2,842,714

ELECTRIC DISCHARGE DEVICES Filed Jan. '7, 1955 WWW 5 w w e J5 w z W. T UWM4 m 6/ FIE-1.6.

United 2,842,714 ELECTRIC DISCHARGE DEVICES Application January 7, 1955, Serial No. 480,576

Claims priority, application Great Britain January 11, 1954 8 Claims. (Cl. 315-39) This invention relates to electric discharge devices of the kind employed in connection with wave guides to act as automatic switches for ultra high frequency energy, and generallyknown as transmit-receive '(T. R.) or transmitter block (T..B.) cells.

In such apparatus, as described in application'Serial No. 258,851, filed November 29, 1951, by William Joseph Scott, now U. S. Patent No. 2,813,226, dated November 12, 1957, it is usual to provide a gap across which it isrequired to permit an electric discharge to take place, in predetermined conditions; in the arrangements disclosedinthe above-mentioned specification, a gap is pres- ;ent between main electrodesQone of which is hollow and has mounted concentrically within it an auxiliary priming, or keep-alive, electrode to which an ionising potential .isapplied so thatacontinuous, or primer, discharge-takes place, duringoperati'onof the device, between the auxiliaryelectrode and the surrounding main electrode. The gap between the auxiliary electrode and the other of the rnainel'ectrodes was shielded by providing the main electrode with which the auxiliary electrode was associated with a skeleton'tip.

'lt has now been found in such an arrangement, that electrons from the: primer discharge escape into the fringing field regions of the radio frequency gap between the main electrodes where they oscillate and generate noise in circuits coupled-to the radio frequency gap.

The object of the invention is to provide a more complete shielding'than hitherto at and'near the main' gap of the device to prevent electrons originating from the primer dischargegetting-into the fringing field of the gap.

Accoitlingto the invention the tip-of the hollow main electrode with which is associated the auxiliary electrode from which the primer discharge originates, is substantially completely closed to electrons andto-the electric field where primer electrons would otherwise interact with the fringing field except for an area permeable to electrons opposite thew-operating main electrode not larger than the tip of the co-operating main electrode.

T he substantial closing of the tip of the hollow main electrode maybe'effected by forming'it of a tube, the end o-fwhich isdrawn or machined or otherwise modified so as to be of frusto-conical shape, the narrow termination of the frusto-conical portion being of such dimensions as to leave an opening or openings of the required size and shape. Alternatively the tubular hollow main electrode'may be furnished with a .domed or a frusto-conical cap welded, soldered or otherwise secured to the endof the electrode. The cap may be made of wire gauze or like foraminated material the interstices between the meshes of which are closed, exceptforthe tip portion in which the electron-permeable opening is required, by pressing the gauze so as to flatten the wires.

The presence of the wire mesh across the opening in the end of the tip is not detrimental to the operation of the device, in fact its presence is desirable inasmuch as the wires provide electrical continuity to the tip of the hollow electrode and eliminate the undesirable weaker or atent .late the ionisation of the gap between the main electrodes.

The presence of the uniform electric field across the electron permeable opening is so desirable that in the constructions mentioned in the preceding paragraph in which the tip of the hollow main electrode is of continuous metal, foraminous material such as wire gauze, should preferably be provided across the opening. It may be welded to the rim of the opening in the tip of the hollow electrode. Alternatively the frusto-conical cap may be pressed from sheet metal, a slot or perforation being provided in the centre of the cap over an area opposing the tip of the co-operating main electrode.

To enable the invention to be better understood we will now describe, with reference to the accompanying drawings, several embodiments of the same.

In the drawing,

Fig. 1 shows, in cross-sectional view, .a portion of a T.1R. cell of the kind to which the invention relates,

Fig. 2 is an enlarged view of the improved construction of main and primer electrodes of the invention,

Fig. 3 is a modified construction of a similar nature 'to'that shown in Fig. 2,

Fig. 4 is a further modification of the Fig. .2 arrangement, and

Figs. 5 and 6 are sectional views inside and-end elevation ofa further modified form of electrodes in accordance'with the invention. 1

Referring now to Fig. 1, we have here shown in crosssection a rectangular wave guide 10, having arranged across it a diaphragm or iris 11, which is located within a portion of the wave guide sealed from the remainder thereof by spaced walls permeable to electro-magnetic waves to enable the enclosed space to .be evacuated and filled with an ionisable gas such as water vapour. The partition or iris 11 is provided with a resonant slot or aperture 12, the dimenisons of which :are such as to render it resonant at a predetermined frequency of oscilla- :tions to 'bepassed through the wave guide. The resonant aperture .12 has extending across it main coaxial electrodes 15, 14, between the opposite tips of whicha glow discharge is adapted to take place when the energy of the oscillations passing through the wave guide is of a high value. When so energized, the resonant circuit becomes short-circuited and forms a barrier across the waveguide preventing further. passage of wave energy therethrough.

In order to assist in ionisation of the gap between electrodes 13, 14, a continuous or primer glow discharge is caused to take place during operation of the device between the main electrodes 14 and an auxiliary or priming electrode 15, shown in interrupted lines in Fig. 1 and arranged concentrically within the main electrode 14 and insulated therefrom. During operation a direct potential is applied between the auxiliary electrode 15 and the cooperating main electrode 14 with the auxiliary electrode 15 negative to the electrode 14.

The arrangement of the electrodes is shown more clearly in the enlarged sectional diagram of Fig. 2 where it may be noted that the auxiliary electrode 15 extends concentrically within the electrode 14 and is insulated It has been found, as above mentioned, that in the well-known designs in which there was a single large hole to A diameter) not covered with gauze or else large side openings, the electrons from the primer discharge escape into the fringing field regions of the radio frequency gap between the main electrodes where ence to the tip of the they oscillate and generate noise in circuits coupled to the radio frequency gap. The outer fringing radio frequency field is indicated in chain-dotted lines in Fig. 2.

According to the invention this disadvantage is removed by utilizing barrier means provided with small openings therethrough to substantially completely close to electrons and to the radio frequency electric field the tip region of the hollow main electrode 14 by providing it, in the Fig. 2 arrangement, with a frusto-conical cap 17, secured to the end of the main electrode and provided with an electron permeable area consisting of an aperture 18, opposite the co-operating main electrode 13, which is covered with a' foraminated. material 19, such as wire gauze, said aperture being not larger than the tip of the main electrode 13. It has been found that by this means the noise in circuits associated with the tuned aperture is greatly reduced. The holes or interstices in the gauze should be not much greater than .006" square, and preferably less.

In the modified arrangement shown in Fig. 3, the opening in the frusto-conical cap 17 is perforated instead of providing it with a separate covering of foraminated material. The apertures 20 in the tip of the frustoconical cap provide a similar effect to the openings in the wire gauze 19 of the Fig. 2 arrangement.

In the Fig. 4 arrangement the frusto-conical cap 17 is itself made of foratninated material such as wire gauze, the openings in the gauze at the sides of the cap being substantially closed by pressing the wires so that they depart from the circular cross-section and become elongated. It has been found that gauze made from nickel wire and thickly electro-plated with copper can be compressed readily to close the apertures in the gauze when desired. At the opening 18 across the end of the cap the wires are left circular to leave interstices for the discharge to pass through.

Referring now to the arrangement shown in Figs. and 6, in this case the tubular main electrode 14 is formed with a wedge-shaped tip by bevelling the sides of the tube, as indicated at 22 in Fig. 6. The aperture so formed is then closed by a cap 23, having an aperture 24 therein, which is closed by foraminated material such as wire gauze 25. Slots 26 are also preferably provided in the sides of the tubular main electrode 14 so that by observation sideways through the electrode, the position of the auxiliary or primer electrode 15, with refermain electrode 14, may be observed. Slots 26 must be so far from the primer electrode that no objectional escape of electrons takes place into the fringing field.

In the arrangement shown in Figs. 4, 5 and 6, the primer electrode 15 is shown as being completely encircled by a sheath 27 of glass adherent thereto, except for the exposed tip of the primer electrode from which the discharge takes place, but alternative constructions may be used.

The auxiliary electrode may be constructionally combined with a discharge-limiting resistor, as described in co-pending application Serial No. 480,519, filed January 7, 1955, by William Joseph Scott.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A high frequency electric discharge device comprising a sealed envelope adapted to form a part of an permeable to electro-magnetic waves, coaxial spaced main electrodes located between said end walls, said main electrodes having opposed tips between which a radio frequency gap exists and in which gap a glow discharge occurs during operation of the device, at least one of said main electrodes being hollow, and having an open end, ar auxiliary electrode mounted within said hollow main electrode to which an ionising potential is applied during operation of said device to cause a primer discharge to take place between said auxiliary electrode and said hollow main electrode, electrically conductive barrier means located across said open end of the hollow main electrode to provide electrical continuity to the tip thereof, said barrier means having interstitial openings therethrough positioned opposite to said other main electrode through which openings electrons from said primer discharge permeate into said gap.

2. A high frequency electric discharge device as defined in claim 1, wherein the barrier means is formed of a foraminous material.

3. A high frequency electric discharge device as defined in claim 1, wherein the barrier means is formed of a perforated material.

4. A high frequency electric discharge device as defined in claim 1, wherein the barrier means is formed of wire gauze.

5. A high frequency electric discharge device as defined in claim 1, wherein the barrier means is provided with a frusto-conical shape.

6. A high frequency electric discharge device as defined in claim 1, wherein the barrier means comprises a cap having a top and a side wall formed of foraminous material shaped in a frusto-conical configuration, the openings in a portion of said side wall being substantially closed.

7. A high frequecy electric discharge device comprising a sealed envelope adapted to form a part of an electromagnetic wave guide, an ionisable medium filling said envelope, said envelope having spaced apart walls permeable to electromagnetic waves, coaxial spaced main electrodes located between said end walls, said main electrodes having opposed tips between which a radio frequency gap exists and in which gap a glow discharge occurs during operation of the device, said opposed tips positioned within an aperture tuned to the frequency of electromagnetic waves to be passed through said device, at least one of said main electrodes being hollow and having a frusto-conical tip portion provided with an opening in the end thereof, an auxiliary electrode mounted within said hollow main electrode to which an ionising potential is applied during operation of said device to cause a primer discharge to take place between said auxiliary electrode and said hollow main electrode, electrically conductive barrier means located across said opening in the frustohollow main electrode, to provide electrical continuity to the tip thereof, said barrier means having interstitial openings therethrough positioned opposite to said other main electrode through which openings electrons from said primer discharge permeate into said gap.

8. A high frequency electric device as defined in claim 7, wherein the frusto-conical tip portions provided with an opening in the end thereof are formed by a cap secured to the end of said hollow main electrode.

References Cited in the file of this patent UNITED STATES PATENTS 

